Functions inside MongoDB query-CodePudding

I was wondering if was possible to utilize functions inside of MongoDB query by including a function inside of options block or something.

Suppose my database collection has a document:

{"year": "2320"}

And I have function to format this document's year-field:

const reformat = function(input){
 return input.year.substring(2,4) input.year.substring(0,2)
}

And I'll be calling a fetch function like this:

const test = {"year": "2023"}
fetchSomething(test, {}, reformat)

My fetch function looks like this:

async function fetchSomething(query, projection, options){
  const dat = await mongoCli.db("testDB").collection("testCollection").findOne(query, projection, options);
  return dat;
}

So, reformat-function should modify the database's document to match year-attribute of test-variable, not the other way around.

I'm not sure if MongoDB even supports it. Looking at the MongoDB documentation...

CodePudding user response：

All you could do is like this:

const reformat = function(){
 return {allowDiskUse: true}
}

mongoCli.db("testDB").collection("testCollection").findOne(query, projection, reformat());

The option is an input attribute of findOne, you cannot re-define it.

Or you can use $function in aggregation pipeline:

db.mongoCli.aggregate([
   {
      $set: {
         year: {
            $function: {
               body: function (input) {
                  return input.year.substring(2, 4)   input.year.substring(0, 2)
               },
               args: ["$$ROOT"],
               lang: "js"
            }
         }
      }
   }
])

Please be aware, executing JavaScript inside an aggregation expression may decrease performance. Only use the $function operator if the provided pipeline operators cannot fulfill your application's needs. $substrCP and $concat are also available as pipeline operator.

CodePudding user response：

I now realize is that I can accomplish it with a cursor:

const reformat = function(input){
 return input.year.substring(2,4) input.year.substring(0,2)
}

async function fetchSomething(query, options){
  const cursor = await mongoCli.db("testDB").collection("testCollection").find()
  let doc;
  while (await cursor.hasNext()) {
    doc = await cursor.next();
    if (options(doc) == query.year){ break; }
    else { doc = null; }
  }
  cursor.close();
  return doc;
}
const test = {"year": "2023"}
fetchSomething(test, reformat)

Though there might be a better way to do it.